only broadcast using/import to nodes which need it

fix #12381
fix #13999

Author: vtjnash

base/loading.jl

@@ -316,11 +316,16 @@ Windows.
 """
 function require(mod::Symbol)
     _require(mod)
-    # After successfully loading notify downstream consumers
+    # After successfully loading, notify downstream consumers
     if toplevel_load[] && myid() == 1 && nprocs() > 1
         # broadcast top-level import/using from node 1 (only)
         @sync for p in procs()
-            p == 1 || @async remotecall_fetch(_require, p, mod)
+            p == 1 && continue
+            @async remotecall_wait(p) do
+                if !isbindingresolved(Main, mod) || !isdefined(Main, mod)
+                    _require(mod)
+                end
+            end
         end
     end
     for callback in package_callbacks

test/distributed_exec.jl

@@ -1750,9 +1750,6 @@ rmprocs(npids)
 Base.cluster_cookie("foobar") # custom cookie
 npids = addprocs_with_testenv(WorkerArgTester(`--worker=foobar`, false))
 @test remotecall_fetch(myid, npids[1]) == npids[1]
-=======
-end
->>>>>>> include: assume that shared file systems exist for clusters
 
 # Run topology tests last after removing all workers, since a given
 # cluster at any time only supports a single topology.